Phthalide is an organic chemical compound with the molecular formula C8H6O2.

It is a white solid and the simplest benzo lactone.

It is prepared from hydroxymethylbenzoic acid.

[3] The phthalide core is found a variety of more complex chemical compounds including dyes (such as phenolphthalein), fungicides (such as tetrachlorophthalide, often referred to simply as "phthalide"), and natural oils (such as butylphthalide).